I don't think that adequately addresses lukeprog's concern. Even granting that one person shouldn't have the privilege of deciding the world's fate, nor should an AI be created for every human to fight it out (although personally I don't think an would-be FAI designer should rule these out as possible solutions just yet), that leaves many other possibilities for how to decide what to do with the world. I think the proper name for this problem is "should_AI_designer", not "should_human", and you need some other argument to justify the position that it makes sense to talk about "should_human".

I think Eliezer's own argument is given here:

Between neurologically intact humans, there is indeed much cause to hope for overlap and coherence; and a great and reasonable doubt as to whether any present disagreement is really unresolvable, even it seems to be about "values". The obvious reason for hope is the psychological unity of humankind, and the intuitions of symmetry, universalizability, and simplicity that we execute in the course of our moral arguments.